Activated aluminum fuel

ABSTRACT

Aluminum can be used as a fuel source when reacted with water if its native surrounding oxide coating is penetrated with a gallium-based eutectic. When discrete aluminum objects are treated in a heated bath of eutectic, the eutectic penetrates the oxide coating. After the aluminum objects are treated, the aluminum objects can be reacted in a reactor to produce hydrogen which can, for example, react with oxygen in a fuel cell to produce electricity, for use in a variety of applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/171,053, filed Jun. 2, 2016, which claims the benefit of priority ofU.S. Provisional Patent Application No. 62/169,734, filed on Jun. 2,2015, with entire contents of each of these applications herebyincorporated herein by reference.

BACKGROUND

Aluminum has a high energy density (83.8 MJ/L) relative to other metalsand has more than twice the energy density of gasoline (38 MJ/L).Aluminum is also highly reactive with oxidizing agents, making it auseful source of hydrogen. For example, when aluminum is brought intocontact with water, hydrogen is generated through the followingreaction:

2Al+6H₂O⇒2Al(OH)₃+3H₂+Heat  [Eq. 1]

Thus, aluminum has the potential to be a safe source of hydrogen. Undernormal environmental conditions, however, a protective oxide coatingforms on aluminum. This oxide coating forms rapidly and is stable,creating an obstacle to the production of useful amounts of hydrogen andheat from the exposure of aluminum to water.

SUMMARY

An activated aluminum fuel of the present disclosure is a stable andhigh-yielding hydrogen fuel source and, as such, is amenable to use in avariety of hydrogen-based applications in which size, weight,portability, and availability of hydrogen are critical mission factors.For example, the activated aluminum fuel can be stored in a low humidityenvironment, safely transported to a point of hydrogen demand, andreacted with water at the point of demand to produce hydrogen for use inpower generation (e.g., in a hydrogen-powered fuel cell), reducing therisk and complexity otherwise associated with the use of hydrogen as afuel.

In one aspect, a method of fabricating a hydrogen fuel source includesexposing the aluminum object (e.g., a sphere) to a eutectic alloyincluding indium and gallium, diffusing the eutectic alloy from an outersurface of the aluminum object into a volume of the aluminum object, andrecovering at least a portion of the eutectic alloy from the aluminumoxide layer on the outer surface of the aluminum object. The eutecticalloy is diffused through disruptions in the aluminum oxide layer. Asused herein, the term “disruptions” is inclusive of, for example,micro-cracks and nucleation sites.

In some embodiments, the method further includes creating thedisruptions in the aluminum oxide layer on the outer surface of thealuminum object. For example, creating the disruptions in the aluminumoxide layer on the outer surface of the aluminum object can includethermally expanding the aluminum object (e.g., to create mechanicalstress in excess of the tensile yield stress of the aluminum oxidelayer). Thermally expanding the aluminum object can include placing thealuminum object into a bath of the eutectic alloy heated to greater thanabout 75 degrees greater than an initial temperature of the aluminumobject.

In certain embodiments, exposing the aluminum object to the eutecticalloy includes exposing the aluminum object to the eutectic alloyincludes immersing the aluminum object in a bath of the eutectic alloy.

In some embodiments, the outer surface of the aluminum object is exposedto the eutectic alloy for a first predetermined period, and the eutecticalloy diffuses from the outer surface to the volume of the aluminumobject for a second predetermined period. At least a portion of thesecond predetermined period of time occurs outside of the firstpredetermined period such that, for example, the first period of timecan be less than the second period of time.

In certain embodiments, recovering the eutectic alloy from the surfaceof the aluminum object includes centrifuging the aluminum object.

In some embodiments, diffusing the eutectic alloy from the outer surfaceof the aluminum object into the volume of the aluminum object includesdiffusing the eutectic alloy along grain boundaries of aluminum alloy ofthe aluminum object.

In certain embodiments, prior to diffusing the eutectic alloy, thealuminum object is greater than about 87%, by mass, aluminum alloy.

In some embodiments, the aluminum object includes a cold worked aluminumalloy. For example, the cold worked aluminum alloy can be one or more ofextruded and forged.

In certain embodiments, the aluminum object includes a high energy grainboundary having an energy greater than about 0.5 J/m2.

In another aspect, a method of fabricating a hydrogen fuel sourceincludes heating a bath of a eutectic alloy of gallium and indium toabout 100-200 degrees C., placing an aluminum object with a temperaturebelow 100 degrees C. into the bath, leaving the aluminum object in thebath for a predetermined time, and removing the aluminum object from thebath. The predetermined time is of sufficient duration for the eutecticto penetrate the aluminum oxide layer and wet the grain boundariessubstantially throughout the volume of the aluminum object.

In some embodiments, the method further includes recovering at least aportion of the eutectic alloy from an outer surface of the aluminumobject, and returning the recovered eutectic alloy to the heated bath.Additionally or alternatively, the method further includes, with thealuminum object removed from the bath, resting the aluminum object.

In certain embodiments, prior to diffusing the eutectic alloy, thealuminum object is greater than about 90%, by mass, aluminum alloy.Additionally or alternatively, the aluminum object can be a sphere.

In still another aspect, a method for manufacturing a hydrogen fuelsource includes placing aluminum spheres, at room temperature, into abath of liquid indium-gallium eutectic alloy heated to above roomtemperature, stirring the aluminum spheres in the eutectic alloy,removing the aluminum spheres from the bath of the eutectic alloy, andremoving at least a portion of the eutectic alloy from an exteriorsurface of each respective aluminum sphere by one or more ofcentrifuging, vibrating, or tumbling the aluminum spheres. Each aluminumsphere can have a diameter of about 6 mm.

In yet another aspect, a method of fabricating a hydrogen fuel sourceincludes exposing the aluminum object to a eutectic alloy includinggallium, diffusing the eutectic alloy from an outer surface of thealuminum object into a volume of the aluminum object, and recovering atleast a portion of the eutectic alloy from the aluminum oxide layer onthe outer surface of the aluminum object. The eutectic alloy is diffusedthrough an aluminum oxide layer on an outer surface of the aluminumobject. For example, the eutectic alloy is diffused through disruptionsin the aluminum oxide layer on the outer surface of the aluminum object.The eutectic alloy can further include indium and/or tin.

In another aspect, a hydrogen fuel source includes an aluminum objecthaving an outer surface defining a volume of the aluminum object, analuminum oxide layer disposed on the outer surface of the aluminumobject, and a eutectic alloy including gallium and indium, the eutecticalloy diffused within the volume of the aluminum object, and at least aportion of the aluminum oxide layer being free of the eutectic alloy andexposed to air.

In some embodiments, a surface area of the portion of the aluminum oxidelayer that is free of the eutectic alloy is greater than a surface areaof the aluminum oxide layer exposed to air when the hydrogen fuel is ina bath of the eutectic alloy.

In certain embodiments, the diffused eutectic alloy is in a two-phasemixture with the aluminum object.

In some embodiments, the eutectic alloy is greater than zero percent andless than about 3 percent of the combined mass of the eutectic alloy andthe aluminum object.

In certain embodiments, the aluminum object is embrittled such that,under tensile or compressive testing, the aluminum object with theeutectic alloy diffused therethrough fractures at a stress less than theyield stress of the aluminum object in the absence of the eutecticalloy.

In some embodiments, the aluminum object includes a cold worked aluminumalloy.

In still another aspect, a method of testing a hydrogen fuel sourceincludes selecting a subset of aluminum objects from a plurality ofaluminum objects, applying a mechanical force to each aluminum object inthe selected subset; observing the response of each aluminum object inthe subset to the applied mechanical force; and sorting the plurality ofaluminum objects based on the observed responses of the aluminum objectsin the subset. Each aluminum object has an outer surface defining avolume and a eutectic alloy including gallium and indium diffused in thevolume.

In some embodiments, applying a mechanical force to each aluminum objectin the subset includes fracturing each aluminum object in the subset.The applied mechanical load can be a compressive load or a tensile load.

In certain embodiments, observing the response of each aluminum objectin the subset includes determining whether a respective aluminum objectin the subset underwent brittle fracture in response to the appliedmechanical force. For example, this determination can include comparinga fracture stress of the aluminum object with the eutectic alloydiffused therethrough to the yield stress of the aluminum object in theabsence of the eutectic alloy.

In some embodiments, a surface area of the portion of the outer surfaceof the aluminum object that is free of the eutectic alloy is greaterthan a surface area of the aluminum oxide layer exposed to air when thehydrogen fuel is in a bath of the eutectic alloy.

Implementations can include one or more of the following advantages.

In certain implementations, at least a portion of the eutectic alloy onthe surface of the aluminum object is recovered. Thus, as compared tosystems that require the eutectic alloy to be present on the surface ofthe aluminum during a reaction with water, the activated aluminum fuelof the present disclosure requires only a few atomic layers in the grainboundaries of the aluminum and is, therefore, amenable to a wide rangeof applications such as, for example, those applications that requireportability. This also advantageously permits recovery and re-use ofexpensive materials used in the activation process that might otherwiseremain disposed on the exterior surface of the aluminum.

In certain implementations, because the eutectic alloy is diffused alonggrain boundaries of the aluminum alloy of the aluminum object, theutility of the aluminum object as a fuel may be significantly lesssensitive to composition, as compared to aluminum fuel activated andreacted in a bath of eutectic alloy. For example, the aluminum object,prior to diffusion of the eutectic alloy, can be greater than about 87percent by mass aluminum alloy and/or can be cold worked or otherwisesubject to manipulation resulting in high energy grain boundaries.Accordingly, the methods described herein can be used to convert scrapaluminum of relatively low economic value into an activated aluminumfuel of a higher economic value.

In some implementations, because the eutectic alloy is diffused alonggrain boundaries of the aluminum alloy of the aluminum object, theutility of the aluminum object as a fuel may be significantly lesssensitive to shape, as compared to aluminum fuel activated and reactedin a bath of eutectic alloy. For example, the methods described hereincan be used to fabricate stable and high-yielding sources of hydrogen bytreating bulk aluminum in any of various different shapes, as well asthin films or sheets of aluminum (e.g., sheets of aluminum having athickness of greater than about 0.001″ to less than about 0.125″).

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a view of an outer surface of an activated aluminum fuel.

FIG. 2 is a close-up view of the outer surface of the activated aluminumfuel along circle A of FIG. 1.

FIG. 3 is a cross-sectional view of the activated aluminum fuel alongline B-B of FIG. 1.

FIG. 4 is a close-up view of the cross-sectional view of the activatedaluminum along circle C of FIG. 3.

FIG. 5 is a schematic diagram of a system for treating discrete aluminumobjects with a eutectic alloy to form an activated aluminum fuel.

FIG. 6 is a flow chart of a process for treating discrete aluminumobjects using the system of FIG. 5 to form activated aluminum fuel.

FIG. 7 is a flow chart of a process for testing discrete aluminumobjects treated according to the process of FIG. 6.

FIG. 8A is a schematic diagram of a hydrogen-oxygen powered system inwhich activated aluminum fuel is within a reactor.

FIG. 8B is a schematic diagram of a hydrogen-oxygen powered system inwhich activated aluminum fuel is fed into a reactor via a hoppermechanism.

FIG. 8C is a schematic diagram of a hydrogen generation system used tofill a structure.

FIG. 9A is a schematic diagram of a hydrogen generation system for afuel cell, in which a treated coiled strip of activated aluminum fuel isreacted.

FIG. 9B is a hydrogen generation system for a fuel cell, in which aspooled wire of activated aluminum fuel reacts in a reactor.

FIG. 9C is a hydrogen generation system for a fuel cell, in whichactivated aluminum fuel in the shape of rectangular prisms is reacted ina reactor.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIGS. 1-4, an activated aluminum fuel 10 is a hydrogen fuelsource that reacts with water to produce hydrogen and heat. Theactivated aluminum fuel 10 includes a naturally occurring aluminum oxidelayer 12 disposed on an outer surface 14 of an aluminum object 16. Asdescribed in further detail below, a gallium-based eutectic alloy (e.g.,a eutectic alloy of gallium, gallium-indium, gallium-indium-tin, orgallium-tin) extends through disruptions 20 in the aluminum oxide layer12 and is diffused within the volume (or bulk) of the aluminum object16, along eutectic-wetted grain boundaries 18, while at least a portionof the aluminum oxide layer 12 is free of the eutectic alloy and exposedto air. For example, a surface area of the portion of the aluminum oxidelayer 12 that is free of the eutectic alloy and exposed to air can begreater than a surface area of the aluminum oxide layer 12 that isexposed to air when the activated aluminum 10 is in a bath of theeutectic alloy (e.g., floating or submerged in a bath of the eutecticalloy). Because the eutectic alloy contained in the activated aluminumfuel 10 is primarily along the eutectic-wetted grain boundaries 18,where the eutectic alloy can be only a few atomic layers thick, much ofthe eutectic alloy used to prepare the activated aluminum fuel 10 can berecovered. With such a distribution of eutectic alloy primarily alongthe grain boundaries, the activated aluminum fuel 10 remainssubstantially stable in air with low humidity. As used herein, thedisruptions 20 in the aluminum oxide layer 12 includes, for example,cracks in the aluminum oxide layer and/or nucleation sites on thealuminum oxide layer.

In use, when water is brought into contact with the activated aluminumfuel 10, the water contacts the raw aluminum of the aluminum object 16via eutectic wetted grain boundaries 18 such that the reaction of thealuminum fuel with water is spatially distributed with respect to thevolume of the aluminum object 16. The reaction generates hydrogen andheat and results in significant spalling corrosion which exposes more ofthe inner bulk of the aluminum object 16 to the water interface, thusincreasing the surface area available for the reaction as the reactionprogresses. Because the eutectic-wetted grain boundaries 18 extendthroughout the volume of the aluminum object 16, the aluminum object 16may break apart due to this spalling as the reaction with waterprogresses, exposing more of the aluminum object 16 to the water.Without wishing to be bound by theory, it is believed that this is aresult of micro-galvanic cells formed between the aluminum grains (lessnoble metal) and the surrounding eutectic alloy (more noble metal). Whenmore of these cells come into contact with water (thus completing thecircuit) the reaction rate increases. Also, when less water is used theadditional heat causes the rate of reaction to increase (roughly anincrease of 2× for every 10 degrees C.).

As described in further detail below, the presence of the eutectic alloyalong the eutectic wetted grain boundaries 18 while the eutectic alloyis substantially absent from the surface of the aluminum oxide layer 12provides significant advantages with respect to the cost,transportability, and/or stability that make the activated aluminum fuel10 a viable fuel for a variety of applications. Also, since the requiredeutectic alloy in the grains is only a few atoms thick, only a smallamount is needed for activation. For example, as compared to an aluminumobject having a eutectic alloy on an exterior surface of the aluminumobject, the substantial absence of the eutectic alloy from the aluminumoxide layer 12 can result in recycling a higher fraction of the eutecticalloy, thus providing an associated cost reduction. Additionally oralternatively, the reactivity of the activated aluminum fuel 10 withsubstantial absence of the eutectic alloy from the aluminum oxide layer12 on the outer surface 14 of the aluminum object 16 demonstrates thatthe reaction of aluminum and water can be driven with a much smalleramount of eutectic alloy, provided that the eutectic alloy issufficiently distributed along the eutectic-wetted grain boundaries 18.As another example, as compared to an aluminum object reacted with waterin a eutectic bath, the activated aluminum fuel 10 is readilytransportable and, therefore, particularly useful for the production ofhydrogen on-demand and at the point of power generation.

The aluminum object 16 is spherical and, in certain implementations, hasa diameter of less than about 10 mm (e.g., about 6 mm). The spheres canhave directional grains, along the surface of the spheres, resultingfrom extrusion and such directional grains are conducive to grainboundary diffusion into the rest of the aluminum bulk. Additionally oralternatively, the spherical shape can facilitate stirring and othertypes of manipulation of the aluminum object 16 during processing andusage of the fuel. For example, spheres allow easy pouring of the fuelinto containers to be used. In certain implementations, the sphericalshape of the aluminum object 16 facilitates handling during manufactureof the aluminum activated aluminum fuel 10. For example, the sphericalshape of the aluminum object 16 can facilitate removal of the eutecticalloy from the aluminum oxide layer 12 through any of a variety ofmechanical processes including centrifuging, vibrating, and/or tumbling.Additionally or alternatively, as described in further detail below, thelow surface area-to-volume ratio of the spherical aluminum object 10 canadvantageously reduce corrosion (and the resulting waste of aluminum)that occurs on the outer surface 14 of the aluminum object 10 while theeutectic alloy is diffusing into the volume of the aluminum object 10.

Prior to exposure to the eutectic alloy, the aluminum object 16 may begreater than about 85 percent, by mass, aluminum alloy. For example, thealuminum object 16 can be formed of 7075 T6 aluminum alloy, which isabout 87 percent to about 91 percent aluminum alloy by mass.Additionally or alternatively, the aluminum object 16 can be formed ofaluminum alloys having a higher percentage of aluminum than thepercentage found in 7075 aluminum alloy. The remainder of the mass ofthe aluminum object 16, prior to exposure to the eutectic alloy, caninclude impurities. Further, the aluminum alloy of the aluminum object16 can have misaligned grains and, thus, a high energy grain boundary(e.g., greater than about 0.5 J/m²), such as a grain boundarycharacteristic of cold worked aluminum.

The plastic deformation that occurs during cold working canadvantageously yield more surface cracks and initiation sites on theouter surface 14 of the aluminum object 16, where the eutectic alloy candiffuse into the aluminum object 16, as well as a greater distributionof dislocations and high-angle grain boundaries within the otherwiseregular crystalline structure of the aluminum object 16 to facilitatediffusion of a eutectic alloy into and through the interior of thealuminum object 16 during exposure to the eutectic alloy. Cold working,as used herein, includes rolling, bending, shearing, drawing, stamping,forging, extruding, cold shaping, cold forming, and/or otherwiseplastically deforming (such that it does not recrystallize the aluminum)the aluminum object 16 prior to exposure to the eutectic alloy.

Accordingly, the activated aluminum fuel 10 can be made from one or moreof a variety of aluminum alloys that have been cold worked (or havesimilar high energy grain boundaries), and the activated aluminum fuel10 is effective in the presence of impurities. Thus, taken together, itshould be appreciated that the aluminum object 16 used to form theactivated aluminum fuel 10 can be formed from scrap aluminum such as,for example, the aluminum of recycled beverage cans. As compared to analuminum fuel that requires tightly controlled processing parametersand/or composition, the activated aluminum fuel 10 can be formedcost-effectively from a variety of aluminum sources, including aluminumwith a wide variety of alloys, alloy mixes, compositions, andimpurities.

The eutectic alloy may be an indium-gallium eutectic, which is about 22percent by mass indium and about 78 percent by mass gallium, with theindium percentage varying about ±5 percent. In certain implementations,the indium-gallium eutectic additionally includes other metals, such astin. As described in further detail below, because the activatedaluminum fuel 10 includes a small amount of eutectic alloy along theeutectic-wetted grain boundaries 18 and has a surface that is at leastpartially free of the eutectic alloy, it is desirable to recovereutectic alloy that is not along a grain boundary or otherwisecontributing to activation of the activated aluminum fuel 10. Thus, asubstantial portion of the eutectic alloy can be recovered from thesurface of the activated aluminum fuel 10 during the processing of theactivated aluminum fuel 10 and subsequently recycled for further use inthe process.

The diffused eutectic alloy in the eutectic wetted grain boundaries 18of the aluminum object 16 may be in a two-phase mixture with thealuminum object. The presence of the eutectic wetted grain boundaries 18allows the aluminum object 16 to react slowly, remaining substantiallystable, in low-humidity, oxygen environments, but to be highly reactivein water. Thus, presence of the eutectic alloy along the eutectic wettedgrain boundaries 18 facilitates use of the activated aluminum fuel 10outside of a bath of the eutectic alloy, lending itself to stability andportability of the activated aluminum fuel 10. For example, theactivated aluminum fuel 10 can be reacted in the field, away from thelocation in which the activated aluminum fuel 10 was prepared.Additionally or alternatively, where the eutectic alloy is disposedalong the eutectic wetted grain boundaries 18 while being substantiallyabsent from the aluminum oxide layer 12 on the outer surface 14 of thealuminum object 16, the eutectic alloy is efficiently distributedthroughout the activated aluminum fuel 10.

In certain implementations, the eutectic alloy comprises greater than 0percent but less than about 3 percent of the total mass of the activatedaluminum fuel 10. The activated aluminum fuel 10 can yield between 80-95percent ±3 percent of the theoretically expected hydrogen yield,demonstrating that the activated aluminum fuel 10 is a highly efficientsource of hydrogen while containing low concentrations of the eutecticalloy. Given the cost of the eutectic alloy, the efficient distributionof the eutectic alloy within the activated aluminum fuel 10 combinedwith the ability to recycle substantial amounts of the gallium eutecticalloy can be important for the economic viability of the activatedaluminum fuel 10.

The presence of the gallium-containing eutectic alloy along the eutecticwetted grain boundaries 18 results in liquid metal induced embrittlementof the aluminum object 16. Such embrittlement is observed as a change inthe response of the aluminum object 16 to mechanical stress (e.g.,tensile stress and/or compressive stress), as compared to the responseof the material of the aluminum object 16 prior to exposure to thegallium-containing eutectic alloy. For example, the aluminum object 16with sufficient eutectic alloy diffused along the eutectic wetted grainboundaries 18 will undergo brittle fracture, precipitated byintergranular fracture, failing at a stress less than the yield stressof the material of the aluminum object, upon exposure to tensile orcompressive stress, whereas, prior to exposure of the aluminum object 16to the eutectic alloy, the material of the aluminum object 16 would beductile and fail at the yield stress.

The embrittlement of the aluminum object 16 serves as a useful predictorfor the quality of the activated aluminum fuel 10 as a fuel sourcebecause it is related to the degree of diffusion of the eutectic alloyinto the aluminum fuel, and because advantageous for the aluminum object16 to break apart as the reaction with water progresses. For example,previous systems that used bulk structures inherently would not breakapart so readily, which then prevented the desired rapid generation ofhydrogen. That is, the bodies tended not to break apart, but aprotective oxide would reform and deter the production of additionalhydrogen, even with a substantial mass of unreacted aluminum. Thus, asdescribed in further detail below, the embrittlement of the aluminumobject 16 can serve as a useful test for determining whether asufficient amount of eutectic alloy has diffused within the aluminumobject 16 such that the activated aluminum fuel 10 will act as a usefulsource of hydrogen.

The aluminum oxide layer 12 forms on the outer surface 14 of thealuminum object 16 when the aluminum object 16 is in air. The aluminumoxide layer 12 is stable and prevents water from reacting withun-oxidized aluminum of the aluminum object 16 beneath the aluminumoxide layer 12. However, the aluminum oxide layer 12 may includedisruptions 20 that facilitate penetration of the eutectic alloy intothe volume of the aluminum object 16. As used herein, disruptions 20include, for example, micro-cracks and/or nucleation sites. In use, thedisruptions 20 facilitate corresponding water penetration into thealuminum object 16, along the wetted eutectic grain boundaries 18, suchthat the water can react with un-oxidized aluminum underneath the nativesurrounding aluminum oxide layer 12.

Referring now to FIG. 5, an exemplary treatment system 50 that can beused to fabricate activated aluminum fuel (e.g., the activated aluminumfuel 10 of FIGS. 1-4) includes a treatment bath 52, containing aeutectic alloy 53, discrete aluminum objects 54, 55, and 56, and aheater 57. The treatment bath 52 may be disposed on the heater 57. Inuse, the discrete aluminum objects 54, 55, and 56 may be heated to atemperature between 100-200 degrees C., and the discrete aluminumobjects 54, 55, and 56 may be stirred to move the discrete aluminumobjects 54, 55, and 56 to different levels of submersion within thetreatment bath 52 to ensure proper wetting of the aluminum objects 54,55, and 56. As described in further detail below, the time that thealuminum objects 54, 55, and 56 are exposed to the eutectic alloy 53 inthe treatment bath 52 is a parameter that may be controlled to balancethe competing physical processes of diffusion of the eutectic alloy 53into the volume of the aluminum objects 54, 55, and 56 and corrosion ofthe surface of the aluminum objects 54, 55, and 56 by the eutectic alloy53.

Referring to FIG. 6, an exemplary method 60 of fabricating a hydrogenfuel source includes exposing 64 the aluminum object to a eutecticalloy, diffusing 66 the eutectic alloy from an outer surface of thealuminum object into a volume of the aluminum object, and recovering 68at least a portion of the eutectic alloy from the aluminum oxide layeron the surface of the aluminum object. Each step in the exemplary method60 is described in further detail below. It should be appreciated thatthe exemplary method 60 can be used to fabricate, for example, theactivated aluminum fuel 10 (FIGS. 1-4) using the treatment system 50.

Exposing 64 the aluminum object to the eutectic alloy can includeplacing the aluminum object in a bath of the eutectic alloy, which canbe an indium-gallium eutectic alloy. For example, multiple aluminumobjects can be immersed in the bath of the eutectic alloy in a batchprocess, and the bath can be stirred to ensure that the entire surfaceof the aluminum object comes into contact with the eutectic alloy.However, it should be appreciated that exposing 64 the aluminum objectto the eutectic alloy can, additionally or alternatively, includecoating the aluminum object with a layer of eutectic alloy and laterremoving this coating via a centrifuging process after treatment.

The duration of the exposure 64 may be controlled such that the eutecticalloy has sufficient time to penetrate disruptions in the aluminum oxidelayer on the aluminum object. Additionally, the duration of the exposure64 may be controlled such that it is not long enough to allow theeutectic alloy in the bath to corrode significant amounts of thealuminum oxide layer and the aluminum object and, therefore, reduce theyield of the activated aluminum fuel. A suitable intermediate durationmay depend on a variety of factors including, without limitation, theobject size, the object geometry, the object mass, the objecttemperature, bath temperature, ambient temperature, and so forth. Forexample, it has been found that placing a spherical aluminum objecthaving a nominal diameter of 6 mm in the bath of the eutectic alloy forgreater than about 90 minutes and less than about 180 minutes (e.g.,about 120 minutes) balances the competing considerations of sufficientpenetration time and corrosion.

In certain implementations, the bath of the eutectic alloy is heatedabove the temperature of the aluminum object, and the lower temperaturealuminum object can be placed into the heated bath. For example, thealuminum object can be below 100 degrees C. and placed into the bath ofthe eutectic alloy, which has been heated to about 100-200 degrees C.Placing the aluminum object in a heated bath can, in certain instances,result in simultaneous expansion of the aluminum object sufficient tocreate disruptions in the aluminum oxide layer and exposure 64 of thealuminum object to the eutectic alloy through the disruptions in thealuminum oxide layer.

As the aluminum object is exposed 64 to the eutectic alloy, the eutecticalloy may begin to diffuse 66 into the aluminum object through thedisruptions in the aluminum oxide layer. Over time, the eutectic alloymay move in a direction from the outer surface of the aluminum objectand into the grain boundaries (e.g., eutectic wetted grain boundaries 18in FIGS. 1-4) in the volume of the aluminum object. The diffusion 66 ofthe eutectic alloy may occur (e.g., through capillary action) along thegrain boundaries of the aluminum object until the eutectic alloy isdiffused substantially throughout the aluminum object. In view of thediffusion process, symmetry (e.g., in the form of a sphere) of thealuminum object can be advantageous for producing a relatively uniformdistribution of the eutectic alloy throughout the volume of the aluminumobject.

While the diffusion 66 of the eutectic alloy into the aluminum oxidebegins upon exposure 64 of the eutectic alloy to the aluminum object,the diffusion 66 may also continue after the aluminum object has beenremoved from the eutectic alloy. Thus, exposure 64 of the aluminumobject can occur over a first predetermined period, and the diffusion 66of the eutectic alloy into the volume of the aluminum object can occurover a second predetermined period, which may overlap with or beindependent of the exposure window. In general, the second predeterminedperiod is a resting period, during which the aluminum object is not yetoptimally suited for use as a source of hydrogen, and at least a portionof the second predetermined period may occur outside of the firstpredetermined period, e.g., after the object is no longer exposed to theeutectic alloy. Further, in view of the competing processes of diffusioninto the volume of the aluminum object and corrosion on the surface ofthe aluminum object, the first predetermined period may advantageouslybe less than the second predetermined period. For example, the firstpredetermined period associated with the exposure 64 can be about 20minutes to about 180 minutes (e.g., about 120 minutes), while the secondpredetermined period is at least about 24 hours.

In certain implementations, the aluminum object may be thermallyexpanded to exploit the difference in the respective coefficients ofthermal expansion of the aluminum object and the aluminum oxide layerformed on the outer surface of the aluminum object. The coefficients ofthermal expansion for aluminum and aluminum oxide are 2.22×10⁻⁵ m/(m/K)and 5.4×10⁻⁶ m/(m/K), respectively. Thus, given that the aluminum objecthas a greater coefficient of thermal expansion than that of thesurrounding aluminum oxide layer, thermal expansion of the aluminumobject can create stress in the aluminum oxide layer (which does notexpand as readily as aluminum expands) in excess of the tensile strengthof the aluminum oxide layer (e.g., resulting in brittle fracture) toform disruptions in the aluminum oxide layer. Under suitable conditions,this expansion of the aluminum object beyond the tensile strength of thealuminum oxide layer can produce a plurality of disruptions in thealuminum oxide layer.

Given variations in composition of the aluminum object afforded by themethods of the present disclosure, heating the aluminum object togreater than about 30 degrees C. above an initial temperature (e.g.,greater than about 75 degrees C. above an initial temperature) of thealuminum object is believed to be sufficient to disrupt the aluminumoxide layer (e.g., by inducing brittle fracture). For example, atemperature increase of 135 degrees C. (e.g., from 25 degrees C. to 160degrees C.) can cause stress in the aluminum oxide layer in excess ofthe tensile strength of the aluminum oxide layer such that the aluminumoxide layer is physically disrupted. It should be appreciated, however,that other temperature differences sufficient to disrupt the aluminumoxide layer may also or instead be used, and are within the scope of thepresent disclosure. The melting temperature of the aluminum objectrepresents an upper boundary on the amount of heat that can be appliedto the aluminum object to disrupt the aluminum oxide layer. It should befurther appreciated that other methods of disrupting the aluminum oxidelayer (e.g., the creation of nucleation sites on the aluminum oxidelayer) are within the scope of the present disclosure.

Recovering 68 at least a portion of the eutectic alloy from the outersurface of the aluminum oxide layer may include removing the aluminumobject from the bath of the eutectic alloy and, in certainimplementations, allowing the aluminum object to cool. With the aluminumobject removed from the bath of the eutectic alloy and optionallycooled, recovering 68 the eutectic alloy can include mechanicallyremoving a substantial portion of the eutectic alloy from the surface ofthe aluminum object such that at least a portion of a surface area ofthe aluminum object is free of the eutectic alloy and exposed to air. Aloose layer of aluminum oxide or aluminum hydroxide will cover theunderlying aluminum from reacting significantly if kept in air for shortperiods of time. Examples of mechanically removing the eutectic alloyfrom the surface of the aluminum object include one or more ofcentrifuging, vibrating, or tumbling.

Substantially uniformly shaped aluminum objects, such as sphericalaluminum objects, can offer advantages with respect to the removal ofthe eutectic alloy. For example, as compared with shapes that areirregularly shaped and/or have a high surface energy (e.g., aluminumchips), the eutectic alloy can be more easily and effectively removedfrom the surface of a spherical aluminum object with a slightly polishedsurface. Thus, in certain implementations, recovering 68 a substantialportion of the eutectic alloy is achieved by centrifuging aluminumspheres, having a nominal diameter of 6 mm, at about 6000 rpm for about30 seconds.

Given the cost associated with the eutectic alloy, recovering 68 theeutectic alloy can accrue substantial economic benefits, and may includereturning the eutectic alloy to the bath for subsequent processing ofadditional aluminum objects. Because a substantial portion of theeutectic alloy is recovered 68, the amount of eutectic alloy consumed infabricating the activated aluminum fuel corresponds approximately to theeutectic alloy along the grain boundaries of the volume of the aluminumobject.

In one example of the use of the exemplary method 60 to fabricate ahydrogen fuel source, 6 mm diameter aluminum spheres having greater than99 percent aluminum content, by mass, were treated with anindium-gallium eutectic alloy to create an activated aluminum fuelaccording to the following process. A bath of the indium-galliumeutectic alloy was placed on a hot plate, and heated with the hot platetemperature at 150 degrees C. The 6 mm spheres, at room temperature,were placed in the heated bath of the eutectic alloy and stirred for 30minutes. The 6 mm spheres were then removed from the heated bath of theeutectic alloy and centrifuged at 6000 rpm for 30 seconds. The 6 mmspheres were then allowed to rest for 48 hours to achieve an appropriateamount of diffusion of the eutectic alloy within the 6 mm spheres.

In another example, 6 mm spheres were treated according to the sameprocess described with respect to the previous example, except theeutectic alloy used was an indium-gallium-tin eutectic alloy.

The activated aluminum fuel resulting from treatment according to theprevious examples yielded between 80-95 percent ±3 percent of thetheoretically expected hydrogen yield. It should be appreciated that theamount of hydrogen yield observed from the reaction of an activatedaluminum fuel with water can be impacted by variables such as reactiontemperature between water and the activated aluminum fuel, quantity ofwater present during the reaction with the activated aluminum fuel, andtype of water (e.g., distilled water versus tap water).

Referring now to FIG. 7, an exemplary test method 70 for determining thesuitability of an activated aluminum fuel as a source of hydrogenincludes selecting 72 a subset of aluminum objects from a plurality ofaluminum objects, applying 74 a mechanical force to each aluminum objectin the selected subset, observing 76 the response of each aluminumobject to the applied force, and sorting 78 the plurality of aluminumobjects based on the observed response of the aluminum objects in thesubset. Each aluminum object has an outer surface defining a volume, aeutectic alloy including gallium and indium diffused in the volume, andat least a portion of the outer surface free of the eutectic alloy. Inthis context, it is expressly contemplated that there may be someresidue of eutectic alloy on the outer surface according to theeffectiveness and aggressiveness of recovery efforts, althoughpreferably the recovery process will include removing as much of theeutectic as possible without otherwise impacting the mass, stability oruseability of the aluminum fuel. In this context, the exemplary testmethod 70 can be used to determine whether an aluminum object treatedaccording to the exemplary method 60 (FIG. 6) will produce a high yieldof hydrogen and, therefore, can be a useful for quality assurance.

Selecting 72 the subset of aluminum objects from the plurality ofaluminum objects can include selecting the subset from a group ofaluminum objects made in the same batch such that the test results ofthe subset can form at least part of the basis for accepting orrejecting the batch. The number of aluminum objects in the subset canvary and, in certain implementations, depends on the statisticalcertainty required for a particular application. Thus, the subset ofaluminum objects can be any number, provided that the subset is lessthan the plurality of aluminum objects from which the subset isselected. In certain implementations, the selection 72 of the subset ofaluminum objects from the plurality of aluminum objects is random. Insome implementations, the selection 72 of aluminum objects from theplurality of aluminum objects can be based on the visual appearance ofthe aluminum objects.

Applying 74 a mechanical force to each aluminum object in the subset ofaluminum objects includes applying a tensile load and/or a compressiveload to each aluminum object. For example, where the aluminum objectsare spherical, the application 74 of mechanical force may includeapplication of a compressive load. The amount of the mechanical forcemay be selected so that it is sufficient to observe brittle fracture ofan appropriately embrittled aluminum object. In certain implementations,the mechanical force is limited to a force or range of forces below theyield strength of untreated aluminum. In some implementations, themechanical force is increased until the tested aluminum object undergoesmechanical failure.

Observing 76 the response of each aluminum object to the appliedmechanical force includes determining whether the aluminum objectunderwent brittle fracture. For example, the determination of whetherthe aluminum object underwent brittle fracture can be based on acomparison of the stress at which the fracture occurred to the yieldstress of an untreated aluminum reference material (e.g., the samealuminum material used in the treated aluminum object). For example, ifthe tested aluminum object undergoes brittle fracture at a stress thatis less than the yield stress of an untreated aluminum referencematerial, the tested aluminum object can be categorized as havingundergone embrittlement as contemplated herein.

Sorting 78 the plurality of aluminum objects based on the observedresponse of the aluminum objects in the subset to the applied forceincludes separating the aluminum objects that correspond to lots inwhich brittle fracture was observed and those in which brittle fracturewas not observed. Accordingly, the sorting 78 of the plurality ofaluminum objects can serve as a final step in a quality assuranceprocess. In some implementations, the lots in which brittle fracture wasnot observed can be subjected to additional treatment with the eutecticalloy. In another aspect, sorting 78 may include sorting the aluminumobjects into a plurality of ranges or bins according to the appliedforce at which brittle fracture was observed.

Referring now to FIGS. 8A-8C, activated aluminum fuel (e.g., theactivated aluminum fuel 10 of FIGS. 1-4) can be combined with water tocreate hydrogen on-demand in a hydrogen-powered system. As compared tothe challenges of storing and/or transporting hydrogen, the activatedaluminum fuel can be safely and easily stored and transported to thehydrogen-powered system, making it amenable to use in a wide variety ofhydrogen-powered systems.

Referring to FIG. 8A, a reaction system 81 is capable of reactingactivated aluminum fuel with water. A reaction chamber 82 houses thetreated discrete aluminum objects 84. A water inlet 83 allows mediatedamounts of water into the reaction chamber 82 for reaction with thetreated aluminum objects 84. Steam 85 a is generated and will reach theother parts of the treated aluminum objects 84. A hydrogen outlet 85 bhouses a check valve 86 to control the flow of hydrogen and steam out ofthe reaction chamber 82. Because the steam 85 a can cause fuel cells tofail, the steam 85 a is run through a condenser before being directed toa fuel cell 88. The fuel cell 88 also has an oxygen inlet 89 from anoxygen source such as, for example, an oxygen candle. Electric leads 90provide electricity to a system like an autonomous underwater vehicleand an exhaust 91 for water leads from the fuel cell 88.

Referring to FIG. 8B, a reaction system 81′ is similar to the reactionsystem 81. Thus, unless otherwise indicated, an element designated witha primed (′) element number in FIG. 8B is similar to a correspondingelement designated with an unprimed element number in FIG. 8A. Thereaction system 81′ is capable of producing electricity through theintroduction of treated discrete aluminum objects 84′ into a hoppermechanism 82 b and subsequent introduction into a reaction chamber 82 avia a feeding mechanism 85 c.

Referring to FIG. 8C, unless otherwise indicated, an element designatedwith a double primed (″) element number in FIG. 8C is similar to acorresponding element designated with an unprimed element number in FIG.8A. The reaction system 81″ is similar to the reaction system 81, exceptthat the generated hydrogen is instead flowed through piping 92 to aninflatable structure 93 such as, for example, a weather balloon.

While certain implementations have been described, other implementationsare possible.

For example, while the activated aluminum fuel has been described asbeing spherical, other shapes are additionally or alternativelypossible. For example, the aluminum objects can be in the form of one ormore of a bar, a rectangular prism, a thin plate, and a cylinder.Additionally or alternatively, the aluminum object can be a cold formedor a cast shape.

Referring now to FIGS. 9A-9C, the shape of the activated aluminum fuelcan be tied to the design of a reactor in which water is introduced tothe activated aluminum fuel and hydrogen is produced.

Referring now to FIG. 9A, a hydrogen generation system 100 includes acoiled strip of treated aluminum 104 a housed in a reactor 102. A waterinlet 103 provides metered amounts of water to the fuel. Generatedhydrogen and steam are sent through an outlet 105, where the steam isthen condensed in a condenser 106. This hydrogen can then be used forpower generation in a fuel cell or to fill a lighter-than-air structure.

Referring now to FIG. 9B, a hydrogen generation system 100′ is similarto the hydrogen generation system 100 in FIG. 9A. Thus, unlessotherwise, indicated an element designated with a primed (′) elementnumber in FIG. 9B is similar to a corresponding element designed with anunprimed element number in FIG. 9A. The hydrogen generation system 100includes a treated aluminum wire 104 b which is fed into a reactor 102′via a spool of treated aluminum wire 105 b. Steam and hydrogen are thensent through an outlet 105 a to a condensing system, similar to thecondensing system shown in FIG. 9A, to provide pure hydrogen.

Referring now to FIG. 9C, a hydrogen reaction system 100″ is similar tothe hydrogen reaction system 100 in FIG. 10a . Thus, unless otherwiseindicated, an element designated with a double primed (″) element numberin FIG. 9C is similar to a corresponding element designated with anunprimed element number in FIG. 9A. The hydrogen generation system 100″includes treated rectangular prisms 114 c housed in a reactor 112″. Awater inlet 113″ provides metered amounts of water to the treatedrectangular prisms 114 c to react. Steam and hydrogen are then sentthrough a condensing system, similar to the condensing system shown inFIG. 10A, to provide pure hydrogen.

It will be appreciated that the devices, systems, and methods describedabove are set forth by way of example and not of limitation. Absent anexplicit indication to the contrary, the disclosed steps may bemodified, supplemented, omitted, and/or re-ordered without departingfrom the scope of this disclosure. Numerous variations, additions,omissions, and other modifications will be apparent to one of ordinaryskill in the art. In addition, the order or presentation of method stepsin the description and drawings above is not intended to require thisorder of performing the recited steps unless a particular order isexpressly required or otherwise clear from the context.

What is claimed is:
 1. An activated aluminum fuel comprising: a coldworked aluminum object having a surface defining a volume, the coldworked aluminum object containing greater than 87 percent, by mass, of aplastically deformed and non-recrystallized aluminum alloy, the coldworked aluminum object including a high energy grain boundary having anenergy greater than about 0.5 J/m²; a eutectic alloy including galliumand indium, the eutectic alloy within the volume of the cold workedaluminum object; and an aluminum oxide layer along the surface of thecold worked aluminum object, the aluminum oxide layer having disruptionspenetrable by water to reach at least a portion of the eutectic alloy inthe volume of the cold worked aluminum object.
 2. The activated aluminumfuel of claim 1, wherein the eutectic alloy is in a two-phase mixturewith the aluminum object.
 3. The activated aluminum fuel of claim 1,wherein the eutectic alloy is greater than zero percent and less thanabout 3 percent of the total mass of the activated aluminum fuel.
 4. Theactivated aluminum fuel of claim 1, wherein the eutectic alloy is about22 percent by mass indium and about 78 percent by mass gallium.
 5. Theactivated aluminum fuel of claim 1, wherein the eutectic alloy furtherincludes tin.
 6. The activated aluminum fuel of claim 1, wherein thecold worked aluminum object has grain boundaries wetted by the eutecticalloy.
 7. The activated aluminum fuel of claim 1, wherein the coldworked aluminum object is a sphere.
 8. The activated aluminum fuel ofclaim 7, wherein the sphere has a diameter of less than about 10 mm. 9.The activated aluminum fuel of claim 1, wherein the cold worked aluminumobject is a spoolable shape.
 10. The activated aluminum fuel of claim 9,wherein the cold worked aluminum object is a wire.
 11. The activatedaluminum fuel of claim 1, wherein the cold worked aluminum objectincludes directional grains.
 12. The activated aluminum fuel of claim 1,wherein at least a portion of the aluminum oxide layer is free of theeutectic alloy.
 13. The activated aluminum fuel of claim 1, wherein thedisruptions in the aluminum oxide layer include microcracks, nucleationsites, or a combination thereof.
 14. An activated aluminum fuelcomprising: a cold worked aluminum object defining a volume, the coldworked aluminum object containing an aluminum alloy, the cold workedaluminum object including a high energy grain boundary having an energygreater than about 0.5 J/m²; and a eutectic alloy including gallium andindium, the eutectic alloy within the volume of the cold worked aluminumobject, wherein the activated aluminum fuel is reactable with water toyield greater than about 80 percent and less than about 95 percent of atheoretical yield of hydrogen.
 15. The activated aluminum fuel of claim14, wherein the eutectic alloy is greater than zero percent and lessthan about 3 percent of the total mass of the activated aluminum fuel.16. The activated aluminum fuel of claim 14, wherein, with the eutecticalloy therein, the cold worked aluminum object is embrittled such that,under tensile or compressive testing, the cold worked aluminum objectwith the eutectic alloy therein fractures at a stress less than theyield stress of the cold worked aluminum object in the absence of theeutectic alloy.
 17. The activated aluminum fuel of claim 14, furthercomprising an aluminum oxide layer disposed on a surface of the coldworked aluminum object.
 18. The activated aluminum fuel of claim 17,wherein at least a portion of the aluminum oxide layer is exposed to airand free of the eutectic alloy.
 19. The activated aluminum fuel of claim14, wherein the volume of the cold worked aluminum object forms asphere.
 20. The activated aluminum fuel of claim 14, wherein the volumeof the cold worked aluminum forms a wire.
 21. The activated aluminumfuel of claim 14, wherein the volume of the cold worked aluminum formsat least one of a sphere, a bar, a rectangular prism, a thin plate, or acylinder.